. Plants and their uses; an introduction to botany. Botany; Botany, Economic. THE LIVERWORTS OR HEPATICS 515 cells each divide into four spores, while the outer cells become some- what thickened to form a protective case or capsule (Fig. 338 Q, R, H). At the same time the basal part of the arehegonium grows apace and may become so thickened as to give additional protection to the spores o'er the winter. When thus developed it is termed a calyp- tra.^ The spores are set free in spring by the breaking down of the coverings about them, and they germinate by producing a row of cells of which the

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. Plants and their uses; an introduction to botany. Botany; Botany, Economic. THE LIVERWORTS OR HEPATICS 515 cells each divide into four spores, while the outer cells become some- what thickened to form a protective case or capsule (Fig. 338 Q, R, H). At the same time the basal part of the arehegonium grows apace and may become so thickened as to give additional protection to the spores o'er the winter. When thus developed it is termed a calyp- tra.^ The spores are set free in spring by the breaking down of the coverings about them, and they germinate by producing a row of cells of which the
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Image ID: RE0TC6
. Plants and their uses; an introduction to botany. Botany; Botany, Economic. THE LIVERWORTS OR HEPATICS 515 cells each divide into four spores, while the outer cells become some- what thickened to form a protective case or capsule (Fig. 338 Q, R, H). At the same time the basal part of the arehegonium grows apace and may become so thickened as to give additional protection to the spores o\'er the winter. When thus developed it is termed a calyp- tra.^ The spores are set free in spring by the breaking down of the coverings about them, and they germinate by producing a row of cells of which the apical one finally develops a thallus like that already described. We have thus in Riccia quite as evident an alternation of generations as we found in Coleochajte, both the gametophyte and the sporophyte being somewhat more highly de- veloped.. Fig. .339.—Crystahvorts. A-C, Riccia glauca (-;"): ^'1. young antheridium; St, stalk. B, .same, older. C, same, still older, showing the many cells, in which motile gametes (spermatozoids) are produced. D, ripe an- theridium of R. minima (^1=-); e, outer cells of thallus; I, air-spaces. E, R.. citiata (~;i), growing-tip cut vertically to show the terminal cell (s) which by its successive divisions produces all the rest of the plant, the pseudo-leaves (b'-ft"") which project from the lower surface of the thallus and hold water for it, and archegonia, very young (a') and full grown (a"), ready for fertilization. (Waldner, Kny.) Both generations are still more highly developed in the umbrella- liverwort (Marchantia, Figs. 340-342), a common species growing on the earth in moist localities. The spores germinate much as in Riccia, but the thalli are always bisexual. At first, however, both forms are essentially alike and resemble a brood-lobed Riccia. From the under side arise numerous unicellular pseudo-roots and many scale-like pseudo-leaves. On the upper surface are often formed numerous brood-bodies of the form shoA

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